(a) Field of the Invention
The present invention relates to a spunbonded filament nonwoven fabric that can be used for an industrial filter, and a method of preparing the same.
(b) Description of the Related Art
Generally, a filter for a gas turbine is one of important parts that extend the life of components of the turbine by preventing damage, such as by contamination, corrosion, erosion, and the like, caused by particulate matter, and is directly related to power generation and efficiency because it improves compression and fuel efficiency.
However, the performance (collecting efficiency, pressure loss, and so on) of common filters changes during long-term use because they are affected by many environmental influences, particularly by weather, and thus the main function of collecting particulate matter is degenerated, physical performance is decreased, and the lifetime for use is shortened.
Recently, fibers that are used for a filter fabric for a gas turbine have been generally classified as cellulose-based fibers, glass fibers, and synthetic fibers. Korean Patent Publication No. 2003-0046424 discloses a product prepared by stacking cellulose and a nano-fiber web, and it has been generally used for a filter fabric for a gas turbine. However, the filter fabric is easily damaged by bad weather factors (for example rain or snow), and thus it is difficult to maintain uniform performance and use it for an extended period of time even though it is superior in its ability to filter dust (hereinafter, collecting efficiency). That is, particle pollutants in the air flow into the components of the turbine through a damaged part of the fabric, and the total efficiency of the filter is deteriorated.
Furthermore, a filter fabric including glass fibers in concert with staple fibers generates dust of small fibers when pleating the same, and it is problematic to use the filter because of the generated dust
Because of the problems, the nonwoven fabric consisting of synthetic fibers is increasingly expected to be used as a nonwoven fabric for a gas turbine filter. However, products or patents regarding the nonwoven fabric for a gas turbine made of synthetic fibers are not yet sufficient.
Furthermore, in the case of a common synthetic fiber filter prepared so as to have a certain denier, there are problems in that the pressure loss is high because dust particles that are initially filtered block the pores of the filter fabric when filtering the air, and the collecting efficiency and the DHC (dust hold capacity) is accordingly degenerated.
Because of the problems, attempts to improve the properties of the collecting efficiency of the nonwoven fabric along with the pressure loss by varying the fiber density of each layer of an air filter or a nonwoven fabric for the same have been undertaken.
For example, Korean Patent Publication No. 2003-0094707 discloses a nonwoven fabric prepared by stacking 2 or more fiber layers, for example an air outlet layer, an intermediate layer, and an air inlet layer, having different densities, and a filter for an engine using the same. Korean Patent Publication No. 2001-0008271 discloses a filter fabric for an air cleaner of which a nonwoven fabric of staple fibers, wherein a dense layer, an intermediate layer, and a bulky layer are combined without a resin adhesive, has one or more density gradients, and a method of preparing the same. Furthermore, Korean Patent Publication No. 2000-0019746 discloses a polyester composite nonwoven fabric for a separator membrane supporting body, including a low density polyester nonwoven fabric prepared by a dry method as an upper layer and a high density polyester nonwoven fabric prepared by a wet method as a lower layer, and that is surface treated by multi-step calendaring.
However, common filters or nonwoven fabrics disclosed above also have limitations in showing sufficient and superior properties as a filter, because their density, volume, and air permeability based on the same of the filament fibers of each of the layers that have a density gradient are not optimized, and thus it is difficult to manifest deep filtration, the pressure loss is large, and they do not have sufficient mechanical strength, and thus the collecting efficiency for dust in the air or the DHC is still insufficient.